1. Field of the Invention
The invention herein relates to devices for cleaning of ships' hulls. More particularly, it relates to hull cleaning devices which are used while the ship remains in the water, either at pierside or at anchor.
2. Description of the Prior Art
It has been known for centuries that the growth of marine organisms on the hull of a ship is adverse to the ship's sailing performance, particularly its potential speed. Many techniques have been used over the years to remove such marine growth from the hulls. In sailing ship days, ships were often careened on the beach to have their hulls scrubbed clean. Since the advent of dry docks, ships can be put into dry dock for hull cleaning. However, use of a dry dock is undesirable, since when a ship is in dry dock for simple hull cleaning, the dry dock cannot be used for service to other ships, particularly repair services for which dry docks are uniquely suited. In addition, in many places dry docks are not available.
Since careening and dry docking are difficult, expensive, and often dangerous to both ship and workers, numerous techniques have been considered to accomplish hull cleaning while the ship remains in the water, either at anchor or secured to a shore structure such as a pier. The simplest technique, that of putting divers down to clean the hull manually, is very slow, labor intensive and dangerous. Consequently, mechanical hull cleaning devices have been developed which move along the hull underwater and mechanically scrub the accumulated marine organisms cleaning propulsion and steering mechanisms. The use of electrical power for these major functions of the device poses substantial problems, however, particularly disengagement of the device from the hull if power fails and potential electrical hazard to the diver/ operator if a short circuit occurs or the diver inadvertently comes into contact with the electrical system.
Several years after the appearance of the electrohydraulic devices, I developed and introduced a much safer and more efficient hull cleaning device entirely powered and controlled hydraulically, with no electrical requirements for any cleaning, steering or propulsion mechanism or function. Devices of this type used readily available hydraulic fluids and have hydraulic pumps mounted out of the water, usually on a pier or the ship's deck. Back-up power to the pumps is readily available so that the diver/operator can safely and efficiently use and control the device without being at risk of electrocution. For the past several years, these devices have proved very successful and have been used by numerous navies and merchant fleets for hull cleaning of many types of warships and merchant ships, including very large vessels such as battleships and supertankers.
However, experience in service has shown that these hydraulic devices, while superior to any other type of hull cleaning device, still have several deficiencies which require time and expense to cope with. For instance, they cannot readily be used at the water line, since the reduced amount of suction created when the device is partially above water is not sufficient to support the weight of the device (a problem also with the electrohydraulic devices). Further, the wheeled propulsion and steering mechanisms of these devices will eventually become clogged with debris from the cleaning and may also suffer corrosion failures. In such cases, the devices must be brought ashore or on deck and mechanisms must be disassembled and replaced, a procedure which is quite difficult and requires substantial rebuilding of the units. In addition, it has been conventional practice that the mounting structures must be open, thereby allowing water into the interior of the unit where corrosion can occur.